1. Field of the Invention
The present invention relates to a motor driving circuit.
2. Description of the Related Art
A voice coil motor is often used as a motor for realizing an auto-focus function of a camera incorporated in a cellular phone. The voice coil motor is a motor in which a movement amount is changed according to a current amount, and a focus distance can be controlled by adjusting a position of a lens in the camera by the movement amount of the voice coil motor.
FIG. 9 is a diagram illustrating a configuration example of a general motor driving circuit for driving a voice coil motor. A motor driving circuit 200 includes a DA converter (DAC) 210 and a driving circuit 220. At the motor driving circuit 200, control is carried out at the driving circuit 220 so that a current amount by a digital signal outputted from a microcomputer 230 is converted to an analog signal at a DAC 210, and the current amount of a voice coil motor 240 becomes the current amount outputted from the DAC 210.
When the voice coil motor 240 is driven using such motor driving circuit 200, a current amount flowing through the voice coil motor 240 needs to be changed according to the position in order to move the lens to a desired position. However, if the current amount of the voice coil motor 240 is rapidly changed, vibration of the voice coil motor 240 is increased, and time till the lens position is stabilized is prolonged. Thus, instead of sudden change of the current amount outputted from the microcomputer 230 to a target value according to a desired position, control of gradual change to the target value is executed in general (See Japanese Patent Laid-Open No. 2006-227101, for example).
However, if the current amount outputted from the microcomputer 230 is changed gradually, processing to appropriately update the current amount at the microcomputer 230 is required, which increases a processing load of the microcomputer 230.